
                        HOW TOR VERSION NUMBERS WORK

1. The Old Way

 Before 0.1.0, versions were of the format:
     MAJOR.MINOR.MICRO(status(PATCHLEVEL))?(-cvs)?
 where MAJOR, MINOR, MICRO, and PATCHLEVEL are numbers, status is one
 of "pre" (for an alpha release), "rc" (for a release candidate), or
 "." for a release.  As a special case, "a.b.c" was equivalent to
 "a.b.c.0".  We compare the elements in order (major, minor, micro,
 status, patchlevel, cvs), with "cvs" preceding non-cvs.

 We would start each development branch with a final version in mind:
 say, "0.0.8".  Our first pre-release would be "0.0.8pre1", followed by
 (for example) "0.0.8pre2-cvs", "0.0.8pre2", "0.0.8pre3-cvs",
 "0.0.8rc1", "0.0.8rc2-cvs", and "0.0.8rc2".  Finally, we'd release
 0.0.8.  The stable CVS branch would then be versioned "0.0.8.1-cvs",
 and any eventual bugfix release would be "0.0.8.1".

2. The New Way

 After 0.1.0, versions are of the format:
    MAJOR.MINOR.MICRO[.PATCHLEVEL][-STATUS_TAG][ (EXTRA_INFO)]*
 The stuff in parentheses is optional.  As before, MAJOR, MINOR, MICRO,
 and PATCHLEVEL are numbers, with an absent number equivalent to 0.
 All versions should be distinguishable purely by those four
 numbers.

 The STATUS_TAG is purely informational, and lets you know how
 stable we think the release is: "alpha" is pretty unstable; "rc" is a
 release candidate; and no tag at all means that we have a final
 release. If the tag ends with "-cvs" or "-dev", you're looking at a
 development snapshot that came after a given release.  If we *do*
 encounter two versions that differ only by status tag, we compare them
 lexically. The STATUS_TAG can't contain whitespace.

 The EXTRA_INFO is also purely informational, often containing information
 about the SCM commit this version came from. It is surrounded by parentheses
 and can't contain whitespace. Unlike the STATUS_TAG this never impacts the way
 that versions should be compared. EXTRA_INFO may appear any number of
 times. Tools should generally not parse EXTRA_INFO entries.

 Now, we start each development branch with (say) 0.1.1.1-alpha.  The
 patchlevel increments consistently as the status tag changes, for
 example, as in: 0.1.1.2-alpha, 0.1.1.3-alpha, 0.1.1.4-rc, 0.1.1.5-rc.
 Eventually, we release 0.1.1.6.  The next patch release is 0.1.1.7.

 Between these releases, CVS is versioned with a -cvs tag: after
 0.1.1.1-alpha comes 0.1.1.1-alpha-cvs, and so on. But starting with
 0.1.2.1-alpha-dev, we switched to SVN and started using the "-dev"
 suffix instead of the "-cvs" suffix.

3. Version status.

  Sometimes we need to determine whether a Tor version is obsolete,
  experimental, or neither, based on a list of recommended versions.  The
  logic is as follows:

   * If a version is listed on the recommended list, then it is
     "recommended".

   * If a version is newer than every recommended version, that version
     is "experimental" or "new".

   * If a version is older than every recommended version, it is
     "obsolete" or "old".

   * The first three components (major,minor,micro) of a version number
     are its "release series".  If a version has other recommended
     versions with the same release series, and the version is newer
     than all such recommended versions, but it is not newer than
     _every_ recommended version, then the version is "new in series".

   * Finally, if none of the above conditions hold, then the version is
     "un-recommended."
